The present invention relates to differential gear mechanisms, and more particularly, to such mechanisms of the type commonly referred to as “locking differentials”. More specifically, the present invention relates to mechanisms of the type also referred to as “mechanical lockers”, i.e., locking differentials in which the locking function occurs in response to the operation of a mechanical device, as opposed to hydraulic actuation or electromagnetic actuation.
A conventional locking differential made by the assignee of the present invention utilizes a flyweight mechanism to initiate the lock-up of the differential clutch, wherein the flyweight mechanism then retards rotation of the cam plate relative to the differential input (i.e., the ring gear and differential case). Locking differentials of the type that utilize a flyweight mechanism to initiate clutch engagement are now well known, and may be made in accordance with the teachings of any one or more of U.S. Pat. Nos. 3,606,803; 5,484,347, and 6,319,166, all of which are assigned to the assignee of the present invention and incorporated herein by reference. However, it should be understood that the present invention is not limited to only locking differentials that are made in accordance with the teachings of the cited patents.
The locking differentials of the type made and sold commercially by the assignee of the present invention have been in widespread commercial usage for many years, and have performed in an extremely satisfactory manner, especially on vehicles which operate, for at least part of their duty cycle, on rough, uneven terrain, or under conditions of poor traction. Such locking differentials perform especially well when the vehicle is operating on what is referred to as a “split-μ” surface, i.e., wherein the drive wheel on one side of the vehicle has fairly good traction, and the drive wheel on the other side of the vehicle has very poor traction. In such operating conditions, the locking differential will engage the locking clutch, thus driving both drive wheels at the input speed to the differential case (i.e., the speed of rotation of the input ring gear).
One situation that has been observed, in which the conventional locking differential does not perform in a satisfactory manner, is when a vehicle equipped with a mechanical locking differential is operating in a condition in which “spin-out” of one of the driving wheels is inherent. For example, if the vehicle is operating with a mini-spare (i.e., a spare tire which, for purposes of saving space in the trunk, is substantially smaller than the “normal” tires), the difference in tire diameter will cause operation of the differential flyweight mechanism, and lock-up of the differential clutch pack, even as the vehicle is operating in a “straight-ahead” mode.